/Engine/Plugins/Runtime/XRBase/Source/XRBase/Public/HeadMountedDisplayFunctionLibrary.h
Get the transform and dimensions of the playable area rectangle. Returns false if none currently specified/available.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category="Input|XRTracking") static bool GetPlayAreaRect ( FTransform & OutTransform, FVector2D & OutRect )